Blue Moons The Blue Moon A "Blue Moon" is the name given to the second full moon in a calendar month. Because there are roughly 29.5 days between full moons, it is unusual for two full moons to "fit" into a 30 or 31 day month (and impossible to fit into a 28 or 29 day month, so February can never have a Blue Moon). The saying "Once in a Blue Moon" means a rare occurrence, and predates the current astronomical use of the term, which is quite recent. In fact, Blue Moons are not all that rare, on average there will be one Blue Moon every 2.5 years. After 1999, the next Blue Moons will be in November 2001; July 2004; and June 2007. The last one before 1999 was in July 1996. The term Blue Moon is believed to have originated in 1883 after the eruption of Krakatoa. The volcano put so much dust in the atmosphere that the Moon actually looked blue in color.

This was so unusual that the term "once in a Blue Moon" was coined. However, Blue Moon was also used in much the same way we use the term "Harvest Moon". There were twelve names for full moons, one for each month, and the name Blue Moon was used in years which had 13 full moons. It referred to the third full moon of the four occuring between an equinox and solstice in that year. A misinterpretation of this led to a Sky and Telescope Magazine "Star Quiz" in July 1943 followed by an article in March 1946 which stated that the second full moon in any calendar month was called a Blue Moon (attributed to the 1937 Maine Farmers' Almanac), and this definition has now become part of the language. The Double Blue Moon of 1999 In January and March of 1999, we had a situation which only takes place about four times a century: two Blue Moons occurring in the same year. The last time this happened was in January and April of 1961 and it will not happen again until January and March of 2018.

A double Blue Moon most commonly occurs in January/March but is also possible in January/April or January/May and only when there is no full moon at all in February. It is also possible to have a Blue Moon in December of one year and March of the next year, again, there is no full moon in the intervening February. See the links below for more details. Full Moons January-March 1999 What Is a Blue Moon? What Is a Blue Moon? By Tim Sharp, Reference Editor | May 20, 2016 06:17pm ET MORE Night sky watcher Tomsajinsa sent in this photo of the blue moon taken in NYC, August 31, 2012. Credit: Tomsajinsa A "Blue Moon" is a fairly infrequent phenomenon involving the appearance of an additional full moon within a given period. But which period — there are two definitions of the term, and one was borne out of a misunderstanding of the other. The older meaning defines a Blue Moon as the third full moon in a season that has four full moons. Called a seasonal Blue Moon, this occurs about every 2.7 years. Why the third moon?

Seasons normally have three full moons, and some of them, for traditional and religious reasons, must occur at specific times of the year. So, the "Moon Before Yule" is always the one before Christmas. The other meaning is that a Blue Moon is the second full moon within a single calendar month. This definition — a monthly Blue Moon — has gained popularity in recent years because of a misinterpretation of an almanac's original definition. Which one is correct? Well, since language and the meaning of words constantly evolve — take your pick. Both are commonly used today. By the newer definition, there was a Blue Moon on Saturday, May 21, 2016 . The next monthly Blue Moon (a second full moon that appears in a single month) will be on Jan. 31, 2018. The next seasonal Blue Moon (when a season has four full moons) will be in the spring of 2019. The third full moon of that season will be on May 18, 2019.

By the way, Blue Moons are not typically blue in color — that happens only, well, once in a Blue Moon, but there is the possibility for a hint of blue in any full moon (more on this below). Origin of the term The phrase "once in a Blue Moon" has been around for more than 400 years, according to Philip Hiscock , a folklorist at the Memorial University of Newfoundland. In a 2012 article in Sky & Telescope magazine, he explained that the earliest use of term was much like saying the moon is made of green cheese — it indicated something absurd. "He would argue that the moon is blue" was similar to saying, "He would argue that black is white." The meaning evolved to something akin to "never," according to Hiscock. "I'll marry you when the moon turns blue" became the equivalent of "I'll marry you when pigs fly." But, never say never. It turns out that the moon can appear bluish, as it did in 1883 after the volcano Krakatoa erupted. Dust in the air acted as a filter, causing sunsets and the moon to turn green and blue all over the world.

Other events such as forest fires and dust storms can cause the moon to turn blue. So, the meaning of "once in a blue moon" changed from "never" to "rarely," according to Hiscock. When does a Blue Moon occur? Now we get to the contradictory definitions of Blue Moon. The calendrical meaning for the term Blue Moon has been traced back to the now-defunct Maine Farmer's Almanac as far back as the mid-1800s. On the page for August 1937, the almanac explained that the moon "usually comes full 12 times in a year, three times for each season. Occasionally, however, there will come a year when there are 13 full moons during a year, not the usual 12. And that extra full moon also meant that one of the four seasons would contain four full moons instead of the usual three." The almanac followed certain rules for what to call each moon. For example, the last full moon of winter had to fall during Lent; it was called the Lenten Moon.

The first full moon of spring was called the Egg Moon — or Easter Moon, or Paschal Moon — and had to fall within the week before Easter. There was also the Moon Before Yule and the Moon After Yule. So when a particular season had four moons, the third was dubbed a Blue Moon, so that the other full moons could occur at the proper times relative to the solstices and equinoxes. Second definition But what about the definition that many people have heard — that a Blue Moon is the second full month in a single month? That came from a misinterpretation of the original definition. In the Sky & Telescope article, Hiscock helped figure out where this meaning came from. He said that in a question-and-answer column from the July 1943 issue of Sky & Telescope, writer Lawrence J. LaFleur referenced the Maine Farmer's Almanac definition. LaFleur correctly quoted the almanac's account, but he made one important omission: He never specified any dates for the Blue Moon. In 1946, James Hugh Pruett, an amateur astronomer, was writing in Sky & Telescope magazine and repeated some of LaFleur's comments.

Pruett made an incorrect assumption about how the term had been used in the almanac, according to Hiscock. Pruett wrote, "Seven times in 19 years there were — and still are — 13 full moons in a year. This gives 11 months with one full moon each and one with two. This second in a month, so I interpret it, was called Blue Moon." Hiscock explained that Pruett must not have had the 1937 almanac handy, or he would have noticed that the Blue Moon fell on Aug. 21 (obviously not the second full moon that month) and that 1937 had only 12 full moons. Sky & Telescope adopted Pruett's new definition, and the column was used as a source for a nationally syndicated radio program in 1980, which, according to Hiscock, is when this definition gained widespread use. Today, either definition of "Blue Moon" is considered valid. As Texas astronomer Donald W.

Olson wrote in a 2006 column for the magazine, "With two decades of popular usage behind it, the second-full-moon-in-a-month (mis)interpretation is like a genie that can't be forced back into its bottle. But that's not necessarily a bad thing." Additional resources What is a Blue Moon? | Astronomy Essentials | EarthSky What is a Blue Moon? By Bruce McClure and Deborah Byrd in Astronomy Essentials | May 16, 2016 The next Blue Moon (second full moon in one calendar month) will be on January 31, 2018. Most Blue Moons are not blue in color. This photo of a moon among fast-moving clouds was created using special filters. Image via EarthSky Facebook friend Jv Noriega. In recent years, people have been using the name Blue Moon for the second of two full moons in a single calendar month. An older definition says a Blue Moon is the third of four full moons in a single season. Someday, you might see an actual blue-colored moon. The term once in a blue moon used to mean something rare.

Now that the rules for naming Blue Moons include several different possibilities, Blue Moons are pretty common! The next Blue Moon (second full moon in one calendar month) will be on January 31, 2018. Follow the links below to learn more about Blue Moons: Can there be two Blue Moons in a single calendar year? Desert Blue Moon from our friend Priya Kumar in Oman. August, 2012. Thank you, Priya! Blue Moon as third full moon of four in a season. The Maine Farmer’s Almanac defined a Blue Moon as an extra full moon that occurred in a season. One season – winter, spring, fall, summer – typically has three full moons. If a season has four full moons, then the third full moon may be called a Blue Moon. There was a Blue Moon by this definition happened on November 21, 2010 . Another occurred on August 20-21, 2013. It last happened on May 21, 2016, and – on that night – the moon was near the red planet Mars!

On the night of May 21, 2016, many will call the moon a Blue Moon. It’ll be blue in name only. But on that night, something cool is happening. The moon will be near red Mars, now nearly at its closest for this two-year period! May 21 Blue Moon was near red Mars. This full Blue Moon and the red planet Mars shone together all night long, from dusk May 21 until dawn May 22. Of course, the moon will be blue in name only. But red Mars will really be noticeably reddish in color, and the full moon and Mars are guaranteed to be spectacular to view on this date. Earth passed between Mars and the sun on May 22. Astronomers call that an opposition of Mars , because Mars was opposite the sun, rising at sunset. Likewise a full moon rises at sunset. And that’s why Mars was near the moon on May 21, when the moon is full and Mars is just one day from opposition . This photo was created using special blue filters, too. Image via EarthSky Facebook friend Jv Noriega.

The next monthly Blue Moon (third of four full moons in one season) will take place on May 18, 2019. Next monthly Blue Moon on January 31, 2018. In recent decades, many people have begun using the name Blue Moon to describe the second full moon of a calendar month. There was a full moon on July 2, 2015. There was another full moon on July 31, 2015. So the July 31, 2015, full moon was called a Blue Moon, according to this definition. The next one will be on January 31, 2018. The time between one full moon and the next is close to the length of a calendar month. So the only time one month can have two full moons is when the first full moon happens in the first few days of the month. This happens every 2-3 years, so these sorts of Blue Moons come about that often.

The idea of a Blue Moon as the second full moon in a month stemmed from the March 1946 issue of Sky and Telescope magazine, which contained an article called “Once in a Blue Moon” by James Hugh Pruett. Pruett was referring to the 1937 Maine Farmer’s Almanac, but he inadvertently simplified the definition. He wrote: Seven times in 19 years there were — and still are — 13 full moons in a year. This gives 11 months with one full moon each and one with two. This second in a month, so I interpret it, was called Blue Moon. Had James Hugh Pruett looked at the actual date of the 1937 Blue Moon, he would have found that it had occurred on August 21, 1937. Also, there were only 12 full moons in 1937. You need 13 full moons in one calendar year to have two full moons in one calendar month. However, that fortuitous oversight gave birth to a new and perfectly understandable definition for Blue Moon.

EarthSky’s Deborah Byrd happened upon a copy of this old 1946 issue of Sky and Telescope in the stacks of the Peridier Library at the University of Texas Astronomy Department in the late 1970s. Afterward, she began using the term Blue Moon to describe the second full moon in a calendar month on the radio. Later, this definition of Blue Moon was also popularized by a book for children by Margot McLoon-Basta and Alice Sigel, called “Kids’ World Almanac of Records and Facts,” published in New York by World Almanac Publications, in 1985. The second-full-moon-in-a-month definition was also used in the board game Trivial Pursuit. Today, it has become part of folklore. What most call a Blue Moon isn't blue in color. It's only Blue in name. This great moon photo from EarthSky Facebook friend Rebecca Lacey in Cambridge, Idaho. Which Blue Moon definition is better? In recent years, a controversy has raged – mainly among purists – about which Blue Moon definition is better.

The idea of a Blue Moon as the third of four in a season may be older than the idea of a Blue Moon as the second full moon in a month. Is it better? Is one definition right and the other wrong? Opinions vary, but, remember, this is folklore. So we, the folk, get to decide. In the 21st century, both sorts of full moons have been called Blue. As the folklorist Phillip Hiscock wrote in his comprehensive article Folklore of the Blue Moon : Old folklore it is not, but real folklore it is. Can a moon be blue in color? There’s one kind of blue moon that is still rare. It’s very rare that you would see a blue-colored moon, although unusual sky conditions – certain-sized particles of dust or smoke – can create them. Blue-colored moons aren’t predictable. So don’t be misled by the photo above. The sorts of moons people commonly call Blue Moons aren’t usually blue. For more about truly blue-colored moons, click here . Enjoying EarthSky so far? Sign up for our free daily newsletter today! Can there be two Blue Moons in a single calendar year? Yes. It last happened in 1999.

There were two full moons in January and two full moons in March and no full moon in February. So both January and March had Blue Moons. The next year of double monthly blue moons is coming up in January and March, 2018 – and then, after that, in January and March, 2037. Very rarely, a monthly Blue Moon (second of two full moons in one calendar month) and a seasonal Blue Moon (third of four full moons in one season) can occur in the same calendar year. But for this to happen, you need 13 full moons in one calendar year AND 13 full moons in between successive December solstices. This will next happen in the year 2048, when a monthly Blue Moon falls on January 31, and a seasonal Blue Moon on August 23. Bottom line: A blue-colored moon is rare. But folklore has defined two different kinds of Blue Moons, and moons that are Blue by name have become pretty common. A Blue Moon can be the second full moon in a month.

We had that sort of Blue Moon on July 31, 2015, and will happen again on January 31, 2018. Or it can be the third of four full moons in a season. That’ll be May 18, 2019. Once in a Blue Moon Once in a Blue Moon Frequently Asked Questions Once in a Blue Moon ... is a common way of saying not very often, but what exactly is a Blue Moon? According to the popular definition, it is the second Full Moon to occur in a single calendar month. The average interval between Full Moons is about 29.5 days, whilst the length of an average month is roughly 30.5 days. This makes it very unlikely that any given month will contain two Full Moons, though it does sometimes happen. On average, there will be 41 months that have two Full Moons in every century, so you could say that once in a Blue Moon actually means once every two-and-a-half years. Blue Moon Calculator Is there a Blue Moon this year? Next year? The year I was born? The Blue Moon Calculator knows the answer!

Frequently Asked Questions (and their answers) Click the button at the right to see a more detailed answer to each question. Isn't your definition of Blue Moon wrong? More Well, yes and no. It's the definition that's currently popular, but it only dates back to 1946. There's an older, traditional meaning that was used in farmers' almanacs in the 19th century. How often is there a Blue Moon by the old definition? More Once every two or three years, just like the new definition, but not in the same years. Where did the expression Blue Moon come from? More It's been part of the English language for four hundred years. During that time, it's had half a dozen different meanings. Does a Blue Moon have any effect on human behaviour? More It has no more effect on human behaviour than any other Full Moon. Does the Moon actually change colour during a Blue Moon? More No, but there have been rare occasions when the Moon really did turn the colour blue. Why is there a bright ring around the Moon? More It's called a halo, and it's caused by ice crystals high in the Earth's atmosphere. Which months have the most Blue Moons?

More As you might expect, the 31-day months are the winners. October, August and July take the top medals. How often does a year have two Blue Moons? More Four or five times in a hundred years. Can a month have no Full Moon? More Sometimes, February misses out on a Full Moon, but it's the only month that can. How often does February not have a Full Moon? More This happens in years with double Blue Moons, so only four or five times in a hundred years. How often is there a Blue Moon (or a Full Moon) on Halloween? More A Full Moon on Halloween must also be a Blue Moon, and it happens five or six times during the 21st century. How accurately can you calculate the time of a Full Moon? More To within a second or so, but the Earth is spinning erratically, which makes long-term predictions much more uncertain. When did the 2015 Blue Moon occur? More July, in all time zones. When did the 2012 Blue Moon occur? More August or September, depending on your timezone. When did the 2009/2010 Blue Moon occur?

More December 2009, January 2010 or March 2010, depending on your timezone. When did the 2007 Blue Moon occur? More May, June or July, depending on your timezone. When did the 2004 Blue Moon occur? More July or August, depending on your timezone. When did the 2001 Blue Moon occur? More October, November or December, depending on your timezone. What about double New Moons? More They occur every two or three years, just like double Full Moons, but fewer people notice them. Who wrote these pages, and why should we believe what we read here? More His name is David Harper. He has a PhD in mathematics and astronomy, and lives near Cambridge, England. He used to be a professional astronomer, but now he just does it for fun. When will the next Blue Moon occur? More We have an interactive Blue Moon Calculator which will tell you whether your favourite year has a Blue Moon. How do I ask a question that isn't on this list? More We would love to hear from you! Copyright © 1998-2015 by David Harper and L.M.

Stockman All Rights Reserved Designed and maintained by Obliquity This month's moon phases and calculator for any day since 1951 | StarDate Online December -- Moon before Yule What is a Blue Moon and when is the next one? Because the time between two full Moons doesn't quite equal a whole month, approximately every three years there are two full Moons in one calendar month. Over the past few decades, the second full Moon has come to be known as a "blue Moon." The next time two full Moons occur in the same month (as seen from the United States) will be July 2015. The most recent "blue Moon" occurred in August 2012. On average, there's a Blue Moon about every 33 months. Blue Moons are rare because the Moon is full every 29 and a half days, so the timing has to be just right to squeeze two full Moons into a calendar month. The timing has to be really precise to fit two Blue Moons into a single year. It can only happen on either side of February, whose 28-day span is short enough time span to have NO full Moons during the month.

The term "blue Moon" has not always been used this way, however. While the exact origin of the phrase remains unclear, it does in fact refer to a rare blue coloring of the Moon caused by high-altitude dust particles. Most sources credit this unusual event, occurring only "once in a blue moon," as the true progenitor of the colorful phrase. Why do we always see the same side of the Moon from Earth? The Moon always shows us the same face because Earth's gravity has slowed down the Moon's rotational speed. The Moon takes as much time to rotate once on its axis as it takes to complete one orbit of Earth. (Both are about 27.3 Earth days.) In other words, the Moon rotates enough each day to compensate for the angle it sweeps out in its orbit around Earth. Gravitational forces between Earth and the Moon drain the pair of their rotational energy. We see the effect of the Moon in the ocean tides. Likewise, Earth's gravity creates a detectable bulge -- a 60-foot land tide -- on the Moon.

Eons from now, the same sides of Earth and Moon may forever face each other, as if dancing hand in hand, though the Sun may balloon into a red giant, destroying Earth and the Moon, before this happens. When does the young Moon first become visible in the evening sky? There is no real formula for determining the visibility of the young Moon. It depends on several factors: the angle of the ecliptic (the Moon's path across the sky) with respect to the horizon, the clarity of the sky (how much dust and pollution gunks it up), and even the keenness of the observer's eyesight. The young Moon becomes visible to the unaided eye much earlier at times when the ecliptic is perpendicular to the horizon, and the Moon pops straight up into the sky. In these cases, it may be possible to see the Moon as little as 24 hours after it was new, although every hour beyond that greatly increases the chances of spotting it. When the ecliptic is at a low angle to the horizon, and the Moon moves almost parallel to the horizon as it rises, the Moon probably doesn't become visible until at least 36 hours past new.

The record for the earliest claimed sighting of the young crescent Moon is around 19 hours, although most experts are suspicious of any claims of times less than about 24 hours. More about Full Moons of 2015: Their Names and Meanings Full Moons of 2015: Their Names and Meanings By Joe Rao, SPACE.com Skywatching Columnist | January 15, 2015 07:27am ET MORE Astronaut Terry Virts took this image of the full moon setting from the ISS. Credit: NASA/Terry Virts While most full moons of the year look similar, they each have unique names. Full moon names date back to Native Americans, living in what is now the northern and eastern United States. Those tribes of a few hundred years ago kept track of the seasons by giving distinctive names to each recurring full moon. Their names were applied to the entire month in which each occurred. There were some variations in the moon names, but in general, the same ones were used among the Algonquin tribes from New England on west to Lake Superior. European settlers followed their own customs and created some of their own names.

Since the lunar month is roughly 29.5 days in length on average, the dates of the full moon shift from year to year. [ 10 Stargazing Events in 2015 ] Here are the names, dates and times of every full moon in 2015: Full Wolf Moon, Jan. 4, 11:53 p.m. EST (0453 Jan. 5 GMT) — Amid the freezing cold and deep snows of midwinter, the wolf packs howled hungrily outside Indian villages. It was also known as the Old Moon or the "Moon after Yule." In some tribes, this was the Full Snow Moon, however, most applied that name to the next moon. Full Snow Moon, Feb. 3, 6:09 p.m. EST (2309 GMT) — Usually the heaviest snows fall in this month each year. Hunting becomes very difficult, and hence to some tribes this was the Full Hunger Moon. Full Worm Moon, March 5, 1:05 p.m.

EST (1805 GMT) — In this month, the ground softens and the earthworm casts reappear, inviting the return of the robins. The more northern tribes knew this as the Full Crow Moon, when the cawing of crows signals the end of winter, or the Full Crust Moon because the snow cover becomes crusted from thawing by day and freezing at night. The Full Sap Moon, marking the time of tapping maple trees, is another variation. Full Pink Moon, April 4, 8:06 a.m. EDT (1206 GMT) —The wild ground phlox is one of the earliest widespread flowers of the spring. Other names for this moon were the Full Sprouting Grass Moon, the Egg Moon and — among coastal tribes — the Full Fish Moon, when the shad came upstream to spawn. This month will also feature a total lunar eclipse , which is set to occur early in the morning with the duration of totality lasting less than 5 minutes. Across the eastern half of the United States, the moon will appear to set while it is progressing into the Earth’s dark shadow.

From Minnesota south to Louisiana, the moon will set during the very short total phase, while for much of the western United States the moon will be exiting the umbra when it sets. This is also the Paschal Full Moon — the first full moon of the spring season. The first Sunday following the Paschal Moon is Easter Sunday, which indeed will be observed the very next day on Sunday, April 5. Full Flower Moon, May 3, 11:42 p.m. EDT (0342 May 4 GMT) —Flowers are abundant everywhere in May. It was also known as the Full Corn Planting Moon or the Milk Moon. Full Strawberry Moon, June 2, 12:19 p.m. EDT (1519 GMT) — Europeans called it the Rose Moon. Full Buck Moon, July 1, 10:20 p.m. EDT (1420 GMT) —In July, the new antlers of buck deer push out from their foreheads in coatings of velvety fur. It was also often called the Full Thunder Moon, thunderstorms being now most frequent. Sometimes it is also called the Full Hay Moon.

[ See amazing photos of a total lunar eclipse ] Blue Moon , July 31, 6:43 a.m. EDT (1043 GMT) — The second full moon occurring within a calendar month is usually given this title. Although the name suggests that to have two full moons in a single month is a rather rare occurrence, it actually occurs once about every three years on average. Full Sturgeon Moon, Aug. 29, 2:35 p.m. EDT (1835 GMT) —In August, the large sturgeon of the Great Lakes and other major bodies of water like Lake Champlain is most readily caught. A few tribes knew it as the Full Red Moon because the moon rises looking reddish through sultry haze. Other names are the Green Corn Moon or Grain Moon. Full Harvest Moon, Sept. 27, 10:50 p.m. EDT (1450 GMT) —The Full Harvest Moon is always the full moon occurring nearest to the Autumnal Equinox. Corn, pumpkins, squash, beans and wild rice — the chief Indian staples — are now ready for gathering.

A total lunar eclipse will be visible in its entirety across the eastern half of North America this month. The eclipse will already be in progress at moonrise across the western half of the country. The U.S. West Coast will see most of the moon within the dark umbra of Earth as it rises. Canada’s Pacific Coast will see the moon in total eclipse at moonrise. This will also be the largest full moon of 2015, as it will also be at perigee later this day, at 7:00 a.m., at a distance of 221,753 miles (356,877 kilometers) from Earth. Full Hunter’s Moon, Oct. 27, 8:05 a.m. EDT (1205 GMT) —With the leaves falling and the deer fattened, it is time to hunt. Since the fields have been reaped, hunters can ride over the stubble, and can more easily see the fox as well as the other animals that have come out to glean — all of which can be caught for a thanksgiving banquet after the harvest. Full Beaver Moon, Nov. 25, 5:44 p.m.

EST (2244 GMT) — Time to set beaver traps before the swamps freeze to ensure a supply of warm winter furs. Another interpretation suggests that the name Beaver Full Moon comes from the fact that the beavers are now active in their preparation for winter. It is also called the Frosty Moon. Full Cold Moon, Dec. 25, 6:11 a.m. EST (1111 GMT) —Among some tribes, this moon was called the Full Long Nights Moon . In this month, the winter cold fastens its grip, and the nights are at their longest and darkest. It is also sometimes called the “Moon before Yule” (Yule is Christmas, and this time the Moon is only just before it). The term Long Night Moon is a doubly appropriate name because the midwinter night is indeed long and the moon is above the horizon a long time. The midwinter full moon takes a high trajectory across the sky because it is opposite to the low sun. Editor's note: If you have an amazing skywatching photo you'd like to share for a possible story or image gallery, please contact managing editor Tariq Malik at spacephotos@space.com .

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, N.Y. Follow us @Spacedotcom , Facebook and Google+ . Original article on Space.com . Once in a Blue Moon? You only have to wait until 31 July – Astronomy Now Once in a Blue Moon? You only have to wait until 31 July By Ade Ashford 29 July 2015 Ade Ashford If you are viewing from the British Isles on the evening Friday, 31 July with a clear sky to the southeast around 10pm BST, you may wish to study the rising full Moon very closely. It is, by one definition at least, a Blue Moon — the second full Moon occurring this month for observers in the UK. The Moon’s size is exaggerated for clarity. AN graphic by Ade Ashford. While I would be extremely surprised for this Friday’s rising full Moon to literally appear blue, it has happened.

On the rare occasions that the Earth’s atmosphere is laden with smoke or dust particles of a size that scatter yellow and red light (approximately one micrometre), the other colours of the spectrum are allowed to pass through, so the Moon — or Sun — can take on a bluish cast. The volcanic eruption of Krakatoa in 1883 led to Blue Moons, as did the eruption of El Chichón in Mexico in 1983. Widespread forest fires in Canada during September 1950 also produced particles of just the right size to scatter longer wavelengths of light for Blue Suns as well as Blue Moons to be seen as far away as the UK. Traditionally, the name Blue Moon was given to the third of four full Moons in a single astronomical season (meaning Blue Moons will occur on 21 May 2016, 18 May 2019 and 22 August 2021), but largely due to the US radio program StarDate in early 1980 and the board game Trivial Pursuit, people have come to use the term Blue Moon to mean the second of two full Moons occurring in a single calendar month.

Full Moons occur every 29.530589 days, on average, which is the lunar synodic period. Since most months are 30 or 31 days long, it’s clearly possible for two full Moons to fit in a single month if the first occurs near the beginning. Since the first full Moon of July 2015 arrived at 3:20am BST on the 2nd, the second full Moon squeezes in at 11:43am BST on July 31st. So, according to the second-full-Moon-in-a-month definition of a Blue Moon, just how often do they occur? If you have a few hours to devote to the task, you can use our online Almanac to generate lunar phases for any calendar date between 1600 and 2400 CE . To spare you the effort for the 21st century, here are the statistics: Between the years 2001 and 2099, there are 41 Blue Moons.

There are three years in which a Blue Moon occurs twice: 2018 (January and March), 2037 (January and March) and 2094 (January and April). Blue Moons can also occur on consecutive years: 2066 and 2067. (Note: these are all UTC timings; the number of events in other time zones will vary considerably.) So, at least in one sense, if the weather is favourable in the British Isles around 10pm BST on Friday, 31 July, you will see a Blue Moon rising in the east-southeast. And if you’re clouded out, console yourself with the thought that you get two opportunities to see the next in 2018! Blue Moons - Origins and History of the Phrase Download Your Free Astrophotography Primer Now from Sky & Telescope! * By: Philip Hiscock | August 24, 2012 August 31st will see the second of two full moons in the same month (the other was on the 1st in North America or on the 2nd in Europe, Africa, Asia and Australia).

You've probably heard the second of those full moons referred to as a "blue moon" — but you might be surprised at the origin of the phrase. "According to old folklore," some people say, the second full Moon in a calendar month is called a "blue Moon." They go on to explain that this is the origin of the expression "once in a blue Moon." But it isn't true! The term "blue Moon" has been around a long time, well over 400 years, but its calendrical meaning has become widespread only in the last 25 years. Blue Moon: A Variety of Meanings Full Moons  are they ever really 'blue?' Courtesy Franz X. Kohlhauf. In fact, the very earliest uses of the term were remarkably like saying the Moon is made of green cheese. Both were obvious absurdities, about which there could be no doubt.

"He would argue the Moon was blue" was taken by the average person of the 16th century as we take "He'd argue that black is white." The concept that a blue Moon was absurd (the first meaning) led eventually to a second meaning, that of "never." The statement "I'll marry you, m'lady, when the Moon is blue!" would not have been taken as a betrothal in the 18th century. But there are also historical examples of the Moon actually turning blue. That's the third meaning — the Moon appearing blue in the sky. When the Indonesian volcano Krakatoa exploded in 1883, its dust turned sunsets green and the Moon blue all around the world for the best part of two years. In 1927, the Indian monsoons were late arriving and the extra-long dry season blew up enough dust for a blue Moon. And Moons in northeastern North America turned blue in 1951 when huge forest fires in western Canada threw smoke particles up into the sky.

So, by the mid-19th century, it was clear that visibly blue Moons, though rare, did happen from time to time — whence the phrase "once in a blue Moon." It meant then exactly what it means today, a fairly infrequent event, not quite regular enough to pinpoint. That's meaning number four, and today it is still the main one. But meaning is a slippery substance, and I know of a half dozen songs that use "blue Moon" as a symbol of sadness and loneliness. The poor crooner's Moon often turns to gold when he gets his love at the end of the song. That's meaning number five: check your old Elvis Presley or Bill Monroe records for more information. And did I mention a slinky blue liquid in a cocktail glass, one that requires curaçao, gin, and perhaps a twist of lemon? That's number six. The Second Full Moon in a Month It's not rare to see two full Moons in a month. Because the Moon's phases are out of sync with our calendar and all the months but February are longer than the lunar cycle of 29½ days, this happens about seven times in every 19 years.

Months have different lengths, so the phenomenon moves around a bit. Click on the image to see the entire chart. Sky & Telescope illustration. All that being said, what is a blue moon ? Finally we arrive at the most recent meaning of all, the second full Moon in a month. I first heard it in 1988. At the end of May that year, when a second full Moon occurred, radio stations and newspapers everywhere carried an item on this bit of "old folklore," as they called it, drawing on an international wire story. Across North America the blue Moon caught the public's imagination. In the following months, restaurants, clothing stores, and bookstores opened under the name "Blue Moon." An artist I know did a set of night landscapes that month; he calls them his Blue Moon series. At the Memorial University of Newfoundland Folklore & Language Archive we get calls from all over, from people wondering about bits of folklore. And that month we got calls about blue Moons. I searched high and low for an earlier example of this usage, or any other name for two full Moons in a single calendar month. But the search was in vain — this meaning seemed to have no history.

I did find information on the other meanings of "blue Moon," but not this one, number seven. Then in December 1990, with another "blue Moon" coming on, I started getting more calls and decided to write about it in the local newspaper. I searched harder this time, exhausting all the usual sources: specialized dictionaries, indexes of proverbial sayings, and regional collections of folklore. A brand-new edition of the huge Oxford English Dictionary had recently come out, but even it omitted this particular meaning. "Blue Moon" seemed to be a truly modern piece of folklore, masquerading as something old. Still Unresolved This Trivial Pursuit card showing, under the heading 'Science and Nature,' the blue Moon question. Sky & Telescope illustration. Then my brother-in-law reminded me that the term was a question in one of the Trivial Pursuit boxes, the Genus II edition published in 1986. I hope the manufacturer of this game is still the fine company for scholars it was then.

They had kept all their files and were able to tell me their source had been a children's book published the previous year, The Kids' World Almanac of Records and Facts (New York, 1985: World Almanac Publications). Where the authors, Margo McLoone-Basta and Alice Siegel, got it, no one seemed to know. Used in this way, the term was certainly very, very local before they included it in their book. It seemed never to have been written down before. Of course, authors sometimes "invent" information to protect themselves against plagiarists. Well, if that were the case they'd already lost, because the new "blue Moon" almost immediately entered the folklore of the modern world. It became as living a meaning as any of its predecessors. Sky & Telescope illustration. During my search it hadn't occurred to me that radio might have played a role. My newspaper column had just gone to the printer when I got a copy of the December 1990 Astronomy. There, Deborah Byrd mentioned the term coming from a March 1946 article in Sky & Telescope (page 3).

(But S&T had got it wrong, too !) Contacting her, I found out she had read it for her National Public Radio program, Star Date, in late January 1980. No doubt that's where the authors of the children's almanac heard it. Clearly, Byrd's radio broadcast got the recent "blue Moon" ball rolling. Our new blue Moon has something of the modern times in it, a technical aspect that most of the earlier meanings lacked. Perhaps that's why it caught on so quickly. It appeals to our modern sensibilities, including our desire to have plausible origins. But any folklorist will tell you that plausibility is the mantle that folklore wears to sneak through history's lines. "Old folklore" it is not, but real folklore it is. Given its present popularity, it may last a long time. CATEGORIES One thought on “Once in a Blue Moon” Once in a blue moon I just love to read this article about once in a blue moon, really such a wonderful stuff can be found only once in a blue moon. Loved it, thanks. Ruth, UK Blue Moon Calendar Blue Moon Calendar ' What is a Blue Moon?

The modern day definition of a Blue Moon is when there are 2 Full Moons in one Month. A Full Moon occurs roughly every 29.5 days and on the rare occasions when the Full Moon falls at the very beginning of a month there is a good chance a Blue Moon will occur at the end of the month. According to this definition the next Blue Moon will occur on January 31, 2018. Year Details > Depending on the exact time of the Blue Moon it is possible that some places in the world don't technicly have a Blue Moon. As an example the Blue Moon on August 31, 2012 occured exactly at 13:58 UT. The Blue Moon will occur on August 31 for South America, North America, Europe, Africa, Asia, India, and Austrialia but New Zealand will just miss out. For New Zealand the Full Moon occurs just past mid-night on September 1st. For exact times of the Full and Blue Moons see the Full Moon Calendar. Original Blue Moon Definition The modern definition of a Blue Moon was derived from an earlier idea of what a Blue Moon was.

This earlier definition says a Blue Moon is when there are 4 Full Moons in a season rather than the usual 3. The Blue moon is the 3rd Full Moon out of the 4. This definition gets a bit complicated and it's origins are murky. One school of thought has to do with the naming of the Full Moons. Many cultures named the Full Moons each month to reflected the times for planting, harvesting or seasonal conditions. When an extra Full Moon was thrown in it was referred to as a Blue Moon to keep the Full Moon names constant throughout the year. Another origin could be from the Christian ecclesiastical calendar. This one gets even more tricky but basically has to do with the idea that there are usually 12 Full Moons in a year. The Full Moons on this calendar were important markers for determining curtain dates such as Easter. When a 13th Full moon was thrown into the year it made things messy so giving it a name allowed the calendar to stay on track.

The idea of a Blue Moon being the extra full moon in a season (or when there were 13 in a year) was widely used in 19th and early 20th center Farmers Almanacs and the more modern version seems to have come from an article written in the 1930's that misinterpreted the Farmers Almanac definition. The article was names "Once in a Blue Moon" and from that point on the term became part of popular culture. Year Details > Is the moon ever the color blue? This is a very rare event but it does happen. There are a few recorded events when forest fires or ash volcanic eruptions have given the moon a bluish color. The moon can also has a blueish color on very cold winter nights when ice crystals in the air form a ring around the moon. Of course the idea of the moon being blue is very subjective and left up to ones own interpretation. Dark Moon An interesting twist to the idea of a Blue Moon is the idea of Dark Moon. Sometimes the reference of a Dark Moon is given when there are 2 new moons is a calendar month, the opposite of a Blue Moon. Other definitions say it is when there is no Full moon is a calendar month.

Neither of these definitions or the term Dark Moon is used very often. Neither has any scientific bases and is more a part of popular culture. To get a better idea of how Blue Moons and Dark moons all fit together, have a look at the Full Moon and New Moon calendar. Full Moon Article, Moon Names Information -- National Geographic A ghostly full moon rises over the Anasazi ruins known as Wukoki in Wupatki National Monument, Arizona. Photograph by David Edwards One of the most dramatic sights in the night sky—and inspiration for poets, artists, and lovers for millennia—full moons captivate us like nothing else. Every month Earth's moon goes through its phases, waning and waxing in its constant transformation from new moon to full moon and back again. Full moons occur every 29.5 days or so as the moon moves to the side of Earth directly opposite the sun, reflecting the sun's rays off its full face and appearing as a brilliant, perfectly circular disk. For millennia, humans have used the movement of the moon to keep track of the passing year and set schedules for hunting, planting, and harvesting.

Ancient cultures the world over have given these full moons names based on the behavior of the plants, animals, or weather during that month. January: Wolf Moon Native Americans and medieval Europeans named January's full moon after the howling of hungry wolves lamenting the midwinter paucity of food. Other names for this month's full moon include old moon and ice moon. February: Snow Moon The typically cold, snowy weather of February in North America earned its full moon the name snow moon. Other common names include storm moon and hunger moon. March: Worm Moon Native Americans called this last full moon of winter the worm moon after the worm trails that would appear in the newly thawed ground. Other names include chaste moon, death moon, crust moon (a reference to snow that would become crusty as it thawed during the day and froze at night), and sap moon, after the tapping of the maple trees. April: Pink Moon Northern Native Americans call April's full moon the pink moon after a species of early blooming wildflower. In other cultures, this moon is called the sprouting grass moon, the egg moon, and the fish moon. May: Flower Moon May's abundant blooms give its full moon the name flower moon in many cultures.

Other names include the hare moon, the corn planting moon, and the milk moon. June: Strawberry Moon In North America, the harvesting of strawberries in June gives that month's full moon its name. Europeans have dubbed it the rose moon, while other cultures named it the hot moon for the beginning of the summer heat. July: Buck Moon Male deer, which shed their antlers every year, begin to regrow them in July, hence the Native American name for July's full moon. Other names include thunder moon, for the month's many summer storms, and hay moon, after the July hay harvest. August: Sturgeon Moon North American fishing tribes called August's full moon the sturgeon moon since the species was abundant during this month. It's also been called the green corn moon, the grain moon, and the red moon for the reddish hue it often takes on in the summer haze. September: Harvest Moon The most familiar named moon, September's harvest moon refers to the time of year after the autumn equinox when crops are gathered. It also refers to the moon's particularly bright appearance and early rise, which lets farmers continue harvesting into the night. Other names include the corn moon and the barley moon.

October: Hunter's Moon The first moon after the harvest moon is the hunter's moon, so named as the preferred month to hunt summer-fattened deer and fox unable to hide in now bare fields. Like the harvest moon, the hunter's moon is also particularly bright and long in the sky, giving hunters the opportunity to stalk prey at night. Other names include the travel moon and the dying grass moon. November: Beaver Moon There is disagreement over the origin of November's beaver moon name. Some say it comes from Native Americans setting beaver traps during this month, while others say the name comes from the heavy activity of beavers building their winter dams. Another name is the frost moon. December: Cold Moon The coming of winter earned December's full moon the name cold moon. Other names include the long night moon and the oak moon. The Blue Moon Each year, the moon completes its final cycle about 11 days before the Earth finishes its orbit around the sun. These days add up, and every two and a half years or so, there is an extra full moon, called a blue moon. The origin of the term is uncertain, and its precise definition has changed over the years.

The term is commonly used today to describe the second full moon of a calendar month, but it was originally the name given to the third full moon of a season containing four full moons.

Question: A second full moon in a single calendar month is now commonly given what name?
Answer: Blue Moon